They had told me they don’t sell the current doubler.
Here’s another email I just got from them:
Victoria Godfrey (Strymon)
Jan 2, 2023, 15:53 AKST
Attached is a screenshot from Eventide’s website stating that the H90 is positive polarity.
We do not sell current doublers, as previously mentioned. You could use this current doubler:
Which would connect to the DC power cables that come with Zuma, which then would connect to our red-tipped polarity reversal cable:
Which would then connect into the H90.
I hope this clears it up for you.